Fusible link



Jan. 21, 1936. C. LA MAR 2,028,720

FUSIBLE LINK Filed Jan. 24, 1934 @JIQIJHI HHIII' IIWIWM IN V EN TOR.

[3 W @MATTORNEY Patented Jan. 21, 1936 UNITED STATES .FUSIBLE LINK Frank 0. La Mar, New York, N. Y., Great Western Fuse Company, New a corporation of Delaware assignor to York, N. Y.,

Application January 24, 1934, Serial No. 708,025

3 Claims.

This invention relates to electrical devices, especially to those electrical devices used for interrupting an electric circuit upon an abnormal flow of current therein, commonly known as cartridge fuses, and more particularly to the fusible link employed therein.

It is well known to those skilled in the cartridge fuse art that the fusible links commonly used in cartridge fuses are defective in that they will not endure for a short time without melting, a flow of current substantially above their rated capacity. This is objectionable because the apparatus and conductors which the fusible link protect are not injured by the flow for a short time of current substantially above the rated capacity of the fuse.

It is also well known to those skilled in the cartridge fuse art that if the well known type of so called, drop out links are used which are 0 formed with a reduced cross-section at either end thereof, the link will melt upon flow for a short time of a substantial overload, but will be melted not at the portions of reduced crosssection but at the very center of the link where the cross-section is generally greatest.

A principal object of this invention is to provide a fusible link of such construction that it will act as a drop out link upon the occurrence of what practically amounts to a dead short circuit, or a. 150% overload, but which will stand for several minutes, in certain rated capacities,

a flow of current substantially greater than the rated capacity of the fuse link, that is, say a 50% overload, and will fuse under such conditions at or about the middle portion of the link. Other objects and advantages will appear as the description of the particular physical embodiments selected to illustrate the invention progresses, and the novel features will be particularly pointed out in the appended claims.

In describing the invention in detail and the particular physical embodiments selected to illustrate the invention, reference will be had to the accompanying drawing and the several views thereon, in which like characters of reference designate like parts throughout the several views, and in which:

Figm'e 1 is a view of a. conventional form of knife blade cartridge fuse with some parts broken away to more clearly show the construction; Fig. 2 is a perspective view of one form of fuse link embodying applicants invention; Fig. 3 is another form of fuse link embodying applicant's Y invention; Fig. 4 is another form of fuse link 56 embodying applicants invention; Fig. 5 is the preferred form of fuse link embodying applicants invention. 1

Figure 1 shows a conventional form of knife blade cartridge fuse showing the fusible link I in place therein connecting the metallic knife blades 2 and 3.

The first form of applicant's invention is shown in Fig. 2 and designated I as it is the form shown in Fig. 1 in connection with the conventional form of cartridge fuse. The fuse link I is, in general, substantially a rectangle of relatively thin metallic material, such as zinc, formed with slots as I and 5 for attaching the link to the knife blades 2 and 3.

The link I is perforated at 6, i, and 8, that is, adjacent either end and substantially in the center. The perforations 6 and 8 are substantially identical and leave on either edge reduced cross-sections-as 9, III, II and I2 all substantially equal. The perforation 1 leaves reduced cross-sections l3 and M which are appreciably larger than cross-sections 9 to 2 inclusive.

When the link I is used in a cartridge fuse, as shown in Fig. l, and is subjected to, say, a 50% overload, it does not melt for about twenty seconds, in certain rated capacities, and when it does melt, it parts at the portions of reduced cross-sections l3 and it. When the fuse link i is subjected to a dead short circuit, or a overload, it acts exactly as a drop out link, that is, it melts at the reduced sections 9, H], H, and 12, so the intermediate portion of the link drops out and is not consumed, so that the cartridge is not subjected to the pressure to which it would be subjected if practically the entire metal portion of the link were vaporized.

Another form of fusible link is shown in Fig. 3 and designated 15. This link is provided with slots 16 and IT for attachment to terminals and with the usual drop out link reduced portions l8 and 19, one at either end. Another reduced cross-section is formed in the link at 20, substantially at the central point thereof. This reduced cross-section 20 is larger than the reduced cross-sections l8 and i9.

This link I5 when subjected to a dead short circuit, or a 150% overload, it is melted at the reduced sections 18 and f9 and the intermediate portion drops out just as in the ordinary drop out link. When the link 15 is subjected to a 50% overload it does not melt for a period a v little longer than the period of the form shown by Fig. 2. When it does melt, however, it does so at the cross-sections 20.

Fig. 4 shows a father form of link. This link 2! is likewise provided with slots 22 and 23 for attachment to terminals and is formed with three cross-sections '24, 25 and 26. The reduced cross-section portions 25 and 25 are substantially identical and adjacent either end of the link. The reduced cross-section 26 is larger than either 241 or 25 and is substantially central of the link. The reduced cross-sections are made by cutting away material of the link inwardly from one edge, that is, the edge 2?.

The link 29 when subjected to a 150% overload will fuse at the points 26 and 25 and the intermediate portion will drop out as in the ordinary drop out link. When subjected to a 50% overload it will melt at the section 26 but not until about four minutes have elapsed, in certain rated capacities, so that it has a very decided time lag.

The fuse link of Fig. 5, designated 28, is the preferred form of applicants fuse link. It, like the others, is substantially a rectangle of thin metal having connection slots 29 and 30. It has the reduced cross-sections 3i and 32 corresponding to the reduced cross-sections 2d and 25 of link 2!. It has also the reduced cross-section 33 which is larger than either cross-sections 3| or 32 and corresponds to the reduced cross-section 26 of, link 2i, but it is not formed by cutting away the metal in from the edge 34 as the metal was cut away from the edge 21 of link 2 I, but is formed by cutting away the metal from the edge 35. The result of cutting away the metal as in applicant's preferred form of time lag fuse link is to cause the current to travel a tortuous path from the end 30 to the end 29.

When the fuse link 28 is subjected to 150% overload its central section drops out by the fusing of the reduced cross-section 3| and 32 just as in the ordinary drop out link. When it is subjected to a 50% overload it melts at the cross-section 33 but not until after practically five minutes have elapsed in certain rated capacities such as those referred to in connection with the description of Fig. 4.

By using links such as those shown in Figs. 2 to 5 inclusive, applicant may obtain a time lag or delay in the fusing of the link upon the flow of a current therethrough of 50% greater than the rated capacity of the fuse as ascertained by ordinary standards, and at the same time obtain a drop out of the central portion of the fuse link upon the flow of current therethrough amounting in effect to a dead short circuit current flow, or to overload.

Applicant is not at all certain that he can explain the reason why he obtains such a pronounced time lag in the case of the form shown aoaavao in Fig. 5 but it is his impression thatthe reason depends upon the fact that the currentfollows -a tortuous path and consequently the large area of the fuse such as the large areas between the cut away portions act more effectually to dissipate the generated heat so that a considerably greater time is required to heat the entire fuse to a temperature such that the cross-section 33 melts.

Applicant's constructions provide the necessary time lag upon a 50% overload and also meet the test of a time lag of about twenty seconds on 150% overload for certain rated capacities.

Although I have particularly described several particular physical embodiments of my invention and explained the operation, construction and principle thereof, nevertheless, I desire to have it understood that the forms selected are merely illustrative, but do not exhaust the possible physical embodiments'of the idea of means underlying my invention. v

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A fusible link, in general a relatively thin flat rectangle formed of metal and provided at each end with means for attachment to terminals, and formed with three reduced crosssection portions, one adjacent each end and one substantially in the center, those at the ends being both produced by removing the metal from one longitudinal edge inwardly, the other being produced by removing the metal from the opposite longitudinal edge inwardly, the end reduced sections being each smaller in cross-section than the other.

2. A drop out link of the type formed with portions of reduced cross-section at either end also formed with a portion of larger reduced cross-section substantially at the center thereof, the center portion of reduced cross-section being arranged so that the flow of current follows a tortuous path from end to end of the link, and the reduced cross-sections at the ends being both-on the same longitudinal edge of the link and on the opposite side from the central reduced section.

3. A drop out link formed substantially as a thin metal rectangle formed with means at each end for attachment toterminals and with reduced cross-sections, one adjacent each of the means for attachment and both adjacent the same longitudinal edge whereby upon the softening of the reduced portion substantially all of the weight of the intermediate portion of the link acts pivotally upon those sections.

FRANK C. LA MAR. 

